This invention relates in general to pressure sensors and in particular to a pressure sensor which is integrated into an electro-hydraulic control unit for an antilock brake system.
An anti-lock brake system (ABS) is often included as standard equipment on new vehicles. When actuated the ABS is operative to control the operation of some or all of the vehicle wheel brakes. A typical ABS, which controls all four vehicle wheels, includes a plurality of normally open and normally closed solenoid valves which are mounted within a control valve body and connected to the vehicle hydraulic brake system. A separate hydraulic source, such as a motor driven pump, is included in the ABS for reapplying hydraulic pressure to the controlled wheel brakes during an ABS braking cycle. The pump is typically included within the control valve body while the pump motor is mounted upon the exterior of the control valve body.
It is also known to provide an ABS for the rear wheels only. Such a system is commonly referred to as a rear wheel anti-lock brake system (RWAL). Typically, RWAL does not include a motor driver pump, but utilizes the vehicle master brake cylinder as a source of pressurized brake fluid. While RWAL has a limited volume of pressurized brake fluid available during an ABS braking cycle, elimination of the pump and pump motor simplifies the system while reducing the cost thereof.
Both four wheel ABS and two wheel RWAL include an electronic control module which has a microprocessor. The control module is electrically coupled to the pump motor, for a four wheel ABS. The control module also is connected to a plurality of solenoid coils associated with the solenoid valves and one or more wheel speed sensors for monitoring the speed and deceleration of the controlled wheels. The control module also is electrically coupled to a pressure sensor which monitors the pressure generated by the vehicle master cylinder. The control module is typically mounted within a removable housing which is attached to the control valve body to form a compact unit which is often referred to as an ABS Electro-hydraulic Control Unit (ECU).
It is known to mount the coils for actuating the solenoid coils within the control module housing. Tubular sleeves which enclose the valve armatures extend from the valve body, forming a seal for the hydraulic brake circuit. When the control module housing is mounted upon the valve body, each of sleeves is received by an associated solenoid coil. Accordingly, the housing can be removed from the valve body for servicing of the control module electronics without opening the hydraulic brake circuit.
During vehicle operation, the microprocessor in the ABS control module continuously receives speed signals from the wheel speed sensors and pressure signals from the pressure sensor. The microprocessor monitors the wheel speed signals and pressure signals for potential wheel lock-up conditions. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to actuate the pump motor, in a four wheel ABS. The microprocessor also is operable to selectively operate the solenoid valves in the valve body to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the driver.
This invention relates to an improved pressure sensor which is integrated into an electro-hydraulic control unit for an anti-lock brake system.
Typically, prior art pressure sensors used in Anti-lock Brake Systems (ABS) are threaded into either a port in the vehicle master cylinder or an external surface of the electro-hydraulic control valve. The external pressure sensor location exposes the sensor to the under-hood operating environment of the vehicle and requires that the sensor be hermetically sealed. Installing a threaded pressure sensor is labor intensive and has a potential for introducing contaminants into the brake fluid. Such pressure sensors also require a dedicated wiring harness which requires an additional manufacturing process step of connecting the harness end to the sensor. Accordingly, it would be desirable to provide an alternate sensor design which eliminates these difficulties.
The present invention contemplates a pressure sensor for a hydraulic control system having a cylindrical base portion which includes a circumferential groove formed therein. The base portion is adapted to be inserted into a bore formed in a hydraulic valve body for the hydraulic control system. A ring of resilient material is disposed within the circumferential groove, the resilient material being adapted to form a seal between the sensor base portion and a wall of the valve body bore. The pressure sensor also includes a pressure sensing device mounted upon the base portion. The base portion can further include a second circumferential groove which carries a spring ring. The spring ring is adapted to cooperate with a complementary groove formed in the valve body bore to retain the sensor in the valve body bore.
Alternately, the second circumferential groove can have a second ring of resilient material disposed therein which is also adapted to form a seal between the pressure sensor base portion and the valve body bore. When the sensor includes two sealing rings, a pressure sensing port is formed in the base portion and the sensed pressure is applied between the rings of resilient material, so that the axial pressures exerted upon the sensor are balanced. The pressure sensor can further include a third circumferential groove formed in the base portion which has a spring ring disposed therein. The spring ring is adapted to cooperate with a complementary groove formed in the valve body bore to retain the sensor in the valve body bore.
It is further contemplated that the pressure sensor includes an axial electrical connector mounted upon the base portion. The connector can include a plurality of electrical connectors. The sensor also includes axial bore formed in the base portion. The axial bore terminates in a diaphragm which carries the pressure sensing device and the bore is adapted to receive pressurized hydraulic fluid. The sensor can further include a cylindrical insert disposed within the axial bore formed in the sensor base portion.
In the preferred embodiment, the pressure sensor is mounted in a hydraulic control system valve body adjacent to a plurality of solenoid valves and enclosed by a removable housing which also carries solenoid coils for the solenoid valves. Also, the electrical connector is a male connector and the housing carries a female connector which cooperates with the male connector to form an electrical connection for the pressure sensing device. The sensor base portion can be formed having a stepped exterior shape with the valve body bore also being stepped. The bore step cooperates with the sensor base portion step to limit the insertion distance of the sensor into the valve body bore.
It is also contemplated that the pressure sensor includes a signal conditioning circuit carried by the sensor base portion. The signal conditioning circuit performs diagnostic tests upon the pressure sensing device and, upon detecting a non-operable pressure sensor, generates an error signal. The diagnostic test can be performed upon initial power up of the sensor and/or during operation of the sensor. In the preferred embodiment, the signal conditioning circuit is connected to a microprocessor included in an anti-lock brake system, the signal conditioning circuit being responsive to a signal from the microprocessor to transmit pressure data to the microprocessor. The sensor also can include a temperature sensor with the signal conditioning circuit being operable to transmit temperature data to the microprocessor.
In addition to being used in an anti-lock brake system, it is contemplated that the pressure sensor also can be used in a traction control system or in a vehicle stability system.
The invention also contemplates a method for installing a sensor into a hydraulic valve body. The method includes providing a pressure sensor having a cylindrical base portion which carries a spring ring in a first circumferential groove formed therein and a ring of resilient material carried in a second circumferential groove formed therein. The pressure sensor is partially inserted into a bore in a valve block for a hydraulic control system until the ring of resilient material forms a seal with the wall of the valve block bore. The pressure sensor is connected to pressure monitoring equipment and the valve block bore is pressurized. The monitoring equipment is observed to confirm operation of the pressure sensor. Finally, the pressure sensor is inserted fully into the valve block bore upon obtaining readings to indicate satisfactory operation of the pressure sensor with the spring ring engaging a circumferential groove formed in the wall of the valve body bore and cooperating therewith to retain the sensor within the valve body bore.